Traditionally, vehicles which operate over adverse terrain, such as rocky terrain, snow covered terrain or swamps, have been skid steered vehicles. Some of these vehicles are track driven, such as bulldozers, loaders, excavators and other heavy industrial vehicles and, others are wheel driven. Many of these wheel driven, skid steered, all terrain vehicles are so constructed as to have low impact, pneumatic wheels engaged with the adverse surface terrain. Examples of such wheeled vehicles capable of being skid steered and intended to have low surface impact are to be found in U.S. Pat. Nos. 3,799,362 and 4,359,116. While the vehicles disclosed in both of these patents are intended to be low ground pressure or surface impact vehicles, they both require lowered middle wheels to facilitate skid steering and both impart greater ground pressure than is desirable for many applications. Additionally, both require chain or mechanical drive systems to all of the axles of these multiple axle vehicles. Chain driven systems are generally undesirable because they need constant attention, suffer from wear, suffer from constant attention to tensioning of the chains and require regular lubrication of the chains. Additionally, these chain driven vehicles also generally suffer from a lack of independent suspension of the individual wheels.
Another chain driven skid steered, wheeled vehicle is disclosed in International Publication No. WO 86/04306. According to the disclosure of this publication, a single hydraulic motor is operable to drive a pair of wheels with there being two pairs of wheels on each side of the vehicle. Because under some operating conditions there is a problem with fluid flow to the hydraulic motor attached to a wheel which has lost contact with the ground, the independently mounted wheels of this vehicle are interconnected by an endless chain so that all of the wheels on one side of the vehicle are made to revolve at the same speed, irrespective of the mode of interconnection of hydraulic motors. Here again, this gives rise to the problem set forth hereinabove relative to wear of the chains and sprockets and maintenance of the appropriate tension of the chain drive system. And, of course, the cost of installation of mechanical driven systems interconnecting the wheels on each side of the vehicle gives rise to increased costs relative to the overall cost of the vehicle.
It has therefore been an objective of this invention to provide a skid steered vehicle having independent suspension of the wheels and characterized by hydraulic drive motors associated with multiple axles of the vehicle so as to minimize surface or ground pressure imparted by the vehicle to the ground surface or terrain over which the vehicle is movable. Still another object of the invention has been to provide such a vehicle which is more effectively and easily capable of skid steering without the need for lowered middle wheels as required in some skid steered vehicles, such as those disclosed in U.S. Pat. Nos. 3,799,362 and 4,359,116.